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Digital archive of theses discussed at the University of Pisa


Thesis etd-04132019-150700

Thesis type
Tesi di dottorato di ricerca
Thesis title
Engineering of bulk and porous PDMS down to the micro/nano scale for sensing and medical applications.
Academic discipline
Course of study
tutor Prof. Barillaro, Giuseppe
controrelatore Prof. Keating, Adrian
controrelatore Prof. Caputo, Domenico
  • CNTs
  • Conductive pressure-strain Sensor; Porous PDMS
  • Optical lens
  • PDMS
  • Silver nanoparticles
Graduation session start date
Release date
PoliDiMetilSiloxane is a silicone elastomer widely used in the manufacture of MEMS devices (Micro Electro Mechanical System) as in lab on chips or Micro Total Analysis System thanks to its properties, such as optical transparency in the UV region and in the visible, low cost of manufacture, easy manufacturing methods and biocompatibility. Academic and industrial research in the field of organic silicones, developed in the twentieth century from the synthesis of the first organic silicone compound developed by Friedel and Crafts in 1863. However, Kipping was the first, in 1901, to mint the term silicone referring to a generic class of materials with polymeric chains that see the alternation of silicon and oxygen in the main chain and containing alkyl groups such as the methyl groups (CH3). Only since 1930, large scale manufacturing processes have been developed, which have led to a reduction in production costs.
In this thesis work on the PDMS the process of realization PDMS in a porous form has been optimized. A comparison between samples in a bulk and porous form in terms of morphology, mechanical properties, and physical-chemical properties was made. In addition, possible applications have been presented which see the use of this polymer in a bulk and porous forms.
Specifically, bulk PDMS was used to make a magnifying lens to be applied to a mobile phone, using a layer of porous silicon as a support. Geometrical and optical properties of the lens have been studied and engineered by varying substrate parameters, such as thickness, current density used to make it, oxidation, and polymer parameters such as the mass used to make the lens and proportions between base and curing agent to compose the polymer. It was also presented the possibility of integrating into the lens DBR (Distributed Bragg Reflectors), made of silicon, in order to provide the lens with light filtering properties.
Porous PDMS offers the possibility of being superficially decorated with nanomaterials that increase its already numerous properties. Two different materials have been used to decorate this polymer: carbon nanotubes and silver nanoparticles.
Decoration with carbon nanotube, made by drop casting makes it as semiconductor material with a resistive behavior whose resistance values change according to the quantity of nanotubes used for decoration and the value of compression deformation applied to the material. Studies of thermoelectric properties have highlighted the possibility of improving thermoelectric efficiency by varying the amount of nanotubes and the applied compression level. This composite material has also been studied as a pressure and strain sensor.
The presence of terminal Si-H groups in the polymer gives the possibility to synthesize silver nanoparticles directly on the surface of the PDMS in both bulk and porous forms. The manufacturing process was studied and optimized in terms of: silver salt precursor used, concentration of the initial silver salt solution and sonication time. Two silver salts were tested (Silver Nitrate and Silver Fluoride), 3 initial concentrations (25, 50, and 100 mM) and 4 sonication times (1, 3, 5, and 8 h). Finally, the antibacterial properties of porous and bulk samples decorated with silver nanoparticles were evaluated.